Advancements in Fast-Ion Tomography with Transport Basis Functions

This work advances fast-ion tomography by introducing a novel technique that not only reconstructs fast-ion distributions but also identifies the specific transport mechanisms shaping them. This capability is achieved by extending the conventional slowing-down basis[1][2] with a set of transport basis functions, enabling the accurate reconstruction of fast-ion distributions even in the presence of complex transport dynamics.

The authors perform velocity space tomographic inversion by integrating data from multiple DIII-D tokamak diagnostics: the Imaging Neutral Particle Analyzer (iNPA) and Fast-ion D-alpha (FIDA). To overcome individual diagnostic limitations, these measurements are combined using a parameter scan balancing diagnostic trustworthiness.

This research extends analytic proof-of-concept models to experimental data. We validate this innovative approach with good accuracy using synthetic fast-ion distributions from TRANSP with a forward model. Finally, tomographic inversions are performed on real DIII-D experimental data, specifically shots with sawteeth that drive fast-ion transport. This work demonstrates a robust framework for quantitatively assessing fast-ion transport in real plasma conditions, allowing for more accurate reconstruction capability in future burning plasmas.

[1] B Madsen et al 2020 Plasma Phys. Control. Fusion 62 115019

[2] B.S. Schmidt et al 2023 Nucl. Fusion 63 076016